Heretofore, a so-called permanent magnet type dynamo electric machine with concentrated winding including a rotor having a plurality of magnetic poles composed of permanent magnets, and a stator having armature windings concentratedly wound around the magnetic poles has been used in various applications. The concentrated winding has the construction in which the armature windings are concentratedly wound around the magnetic poles of the stator and hence automatic winding by a machine is possible therefor. Thus, many permanent magnet type dynamo electric machines with concentrated winding are used mainly for small motors such as servo. In such a small motor, a copper loss, a core loss, and a mechanical loss occupy a majority of the losses, and therefore an eddy current loss caused in the rotor does not become a problem in most cases.
On the other hand, in a large generator whose power generation exceeds several kilowatts, distributed winding was used in many cases in the past. However, the need for the concentrated winding having a small coil end is increasing even in a large generator. For example, in the case where a permanent magnet type synchronous generator is adopted in a wind power generation system, in particular, a gearless type wind power generation system, it can be said that the selection of the concentrated winding is better from a viewpoint that as compared with the distributed winding, in the concentrated winding, a small coil end allows an axial length to be reduced, and moreover, a less copper loss caused in armature windings enables to realize a high efficiency promotion.
As described above, the concentrated winding has a superior advantage in that the coil end is small, and moreover, the automatic winding is possible. However, it has a problem in that an eddy current loss of a rotor due to a magnetomotive force of an armature current becomes larger than that in the distributed winding. Moreover, in recent years, high performance magnets such as a rare earth magnet, each having a high residual magnetic flux density and a high coercive force, have been positively utilized as magnetic poles of a rotor of a large capacity generator. For example, an Nd—Fe—B-based magnet has such characteristics as being high in its electric conductivity, thereby allowing an eddy to easily flow as compared with a ferrite-based magnet.
From the above-mentioned reasons, in the large capacity generator with the concentrated winding, in particular, in the permanent magnet type dynamo electric machine, and the permanent magnet type synchronous generator for wind power generation, each having a rotor with a diameter larger than 1 m, the eddy current loss caused in the rotor reaches a significant level in some cases. Hence, such problems arose that the efficiency of the rotor was remarkably reduced due to the eddy current loss and that a temperature of the rotor rose due to the eddy current loss, incurring the demagnetization of the magnet. In addition, even if the demagnetization was not incurred, the residual magnetic flux density was reduced due to the temperature rise, with the result that the magnetic flux generated by the magnets was reduced. For this reason, more armature current needs to be caused to flow in order to generate the same output power as that in a state free from the temperature rise, and hence there was also a problem in that a copper loss is increased and the efficiency is reduced.
As a method for solving such problems, conventionally, there is a method in which a yoke of the rotor is constructed by a laminated steel plate to thereby reduce the eddy current. In addition, in JP 2001-54271 A, there is disclosed a method in which an iron core of a rotor is constructed by a massive yoke instead of a laminated steel plate, and the yoke is partitioned so that a path of the eddy current is cut off, to thereby reduce the eddy current.
However, there is a problem in that if the lamination structure is adopted for a yoke of a rotor, the cost becomes higher than in the case where an iron core is made of a massive yoke. Moreover, if a massive yoke is partitioned as disclosed in JP 2001-54271 A above, there arise various problems as will be described below. For example, due to an increase in the processing cost, the cost becomes higher as compared with an integral one-piece massive yoke. In addition, in the case where fluctuation occurs in thicknesses of insulating portions provided to the yoke of a rotor, fluctuation also occurs in the flux densities in gap portions of a motor. Thus, there is a fear in that this leads to ununiformity of the electromagnetic force which causes noises and vibration. In addition, there is a problem in that insulating portions for electrically insulating and dividing the yoke are provided in order to partition the yoke, and hence the magnetomotive force is consumed therein, which leads to reduction of the output power of the dynamo electric machine.
As described above, in the conventional permanent magnet type dynamo electric machine, the conventional permanent magnet type synchronous generator for wind power generation, and the like, in order to reduce the eddy current, the construction in which a lamination structure is adopted for a yoke of a rotor and the construction in which a massive yoke is partitioned have been proposed. However, when the lamination structure is adopted, there is a problem in that the cost becomes higher due to the increase in the processing cost. On the other hand, when a massive yoke is partitioned, there arises a problem in that fluctuation occurs in the magnetic flux densities of gap portions of a motor, which leads to ununiformity of the electromagnetic force. Consequently, it can be said that the yoke of the rotor is desirably of an integral type.
The present invention has been made in order to solve the above-mentioned problems associated with the prior art, and it is, therefore, an object of the present invention to obtain a permanent magnet type dynamo electric machine, and a permanent magnet type synchronous generator for wind power generation, each being capable of reducing an eddy current loss of a rotor, while keeping a construction of an integral type for a rotor yoke.